1. Field of the Invention
The present invention relates to a mask for transmitting a light subjected to a projection to a predetermined position and for detecting the light, the mask being suitably applied in an image recognition apparatus such as an OCR (Optical Character Reader).
2. Description of the Prior Art
In the field of optoelectronics, a mask is used to optically extract an optical signal for signal processing, or to optically extract a desired shape from an input image for pattern matching in image recognition by an image recognition apparatus such as an OCR.
In order to prevent a signal mixture and to accurately transmit information, or to prevent blurring of the extracted shape and to obtain a very clear pattern, and further to accurately perform pattern matching of a normalized image, a conventional mask comprises a light-transmitting bright part and a light-reflecting or light-absorbing dark part so as to express binary information. Therefore, the mask pattern must have a very sharp contrast at a boundary between the bright and dark parts.
In general, a mask must be accurately aligned at a position where input light is incident thereon. The light incident position generally must not be deviated.
However, the conventional mask for performing the above-mentioned optical processing has the following drawbacks.
Since a conventional mask has only a binary pattern consisting of the bright and dark parts, only two kinds of information derived from transmission and nontransmission of incident light are obtained. For this reason, light incident on a predetermined position is binarized by the mask, and a photosensor arranged at a position corresponding to that of the mask detects only a binary optical signal.
When light is incident on a position deviated from the proper incident position and is spatially deviated from the mask, light may be incident on the dark part of the mask and is not often detected by the photosensor.